This invention relates to an autothermal reforming catalyst. This invention also relates to a process of producing a fuel gas for a fuel cell wherein hydrocarbons and/or oxygen-containing hydrocarbons are converted to a reformed gas which is composed principally of hydrogen by an autothermal reforming reaction using such a catalyst.
A known process for producing hydrogen from hydrocarbons or oxygen-containing hydrocarbons is an autothermal reforming method which is the combination of an oxidation reaction and a steam reforming reaction. In this process, hydrocarbons or oxygen-containing hydrocarbons, steam, and oxygen or air are introduced into a reactor, and a part of the hydrocarbons or oxygen-containing hydrocarbons is subjected to partial or complete combustion. While the reactor is then heated to a predetermined temperature with the heat generated by the combustion, the remaining hydrocarbons or oxygen-containing hydrocarbons are steam-reformed such that they are converted to a reformed gas which is composed principally of hydrogen. While a catalyst is charged into the reactor, it is required to have a combustion activity and a steam reforming activity.
Examples of such a catalyst are base metal-based catalysts such as nickel, copper, iron, and cobalt, and noble metal-based catalysts such as platinum, rhodium, ruthenium, iridium, and palladium.
The base metal-based catalysts are relatively prone to cause carbon precipitation. Since in order to suppress this, it is necessary to use materials of the catalyst, i.e., hydrocarbons or oxygen-containing hydrocarbons with an excess amount of steam, resulting in a condition where the steam/carbon ratio is high, the activity is inevitably reduced.
On the other hand, since the noble metal-based catalysts hardly cause the precipitation of carbon even under such a condition that the steam/carbon ratio is low, they have an advantage that an excess amount of steam is not required and a reformed gas which is composed principally of hydrogen can be produced at higher efficiency. However, in the case where oxygen coexists at elevated temperatures such as those at which an autothermal reforming reaction is conducted, there arises a problem that the catalyst activity is prone to be reduced due to the condensation or volatilization of the noble metals. Therefor, the noble metal-based catalysts have been demanded to be suppressed in the volatilization or condensation of the noble metals, but such catalysts with a sufficient industrial working life have not been developed yet.
In view of the foregoing, an object of the present invention is to provide a catalyst having a sufficient activity and working life in an autothermal reforming process with maintaining the effect of suppressing the carbon to precipitate at a low steam/carbon ratio.